At the present time the problem of processing and utilizing lead-containing recycable raw material to obtain the maximum recovery of lead is timely, even more so since the percentage of recycable raw material used in the production of lead increases from year to year. An increase in the amount of recovered lead reduces its emission into the environment with gaseous products during the pyrometallurgical method of lead production and with drain water during the hydrometallurgical method of lead production.
A method of recovering lead from a recycable lead-containing raw material is known, reducing the contamination of the environment and increasing the degree of the recovery, which is taught in BR DE 3612491 and includes the following steps.
At first the recycable lead-containing raw material, which is presumed to mean the scrap of lead-sulphuric acid storage batteries, is crushed. Then the aforementioned raw material is separated into fractions--metallized lead, an oxide-sulfate active mass and a polymer material.
The polymer material fraction can comprise lead in an amount up to 6.0% by weight which is present in the fraction as PbO, PbO.sub.2 and PbSO.sub.4.
Then the metallized lead and polymer material fraction are taken out of the process, and the oxide-sulfate fraction is subjected to treatment with a solution comprising Na.sup.+, OH.sup.-, CO.sub.3.sup.2-, and SO.sub.4.sup.2- ions with pH&gt;10, in two steps. During the first step partial desulphurization of the oxide-sulfate fraction takes place in a suspension comprising a solution of sodium sulfate Na.sub.2 SO.sub.4 with pH=6-7, resulting in the absence of lead in the solution, and solid PbO, PbO.sub.2, PbSO.sub.4 particles. Then the obtained suspension is filtered. As a result a solution of sodium sulfate Na.sub.2 SO.sub.4 and solid PbO, PbO.sub.2 and PbSO.sub.4 particles are obtained. After the first step the Na.sub.2 SO.sub.4 solution is subjected to evaporation and an anhydrous Na.sub.2 SO.sub.4 is obtained, which is taken out of the process.
The final desulphurization of the oxide-sulfate fraction takes place during the second step by treating the solid particles of PbO, PbO.sub.2 and PbSO.sub.4 with a solution of NaOH, in particular sulphur as an SO.sub.4.sup.2- ion passes into the alkaline solution, while the solid PbO and PbO.sub.2 particles are taken out of the process during the reduction smelting in the presence of coke.
Now Na.sup.+, SO.sub.4.sup.2-, /Pb(OH).sub.4.sup.2 /.sup.2--, OH.sup.- ions are present in the alkaline solution. The aforementioned solution is fed for carbonization, in particular, flue gas comprising CO.sub.2 is blown through the solution. A suspension is obtained as a result of the carbonization, which is a mixture of a liquid phase comprising Na.sup.+, OH.sup.-, CO.sub.3.sup.2-, SO.sub.4.sup.2- ions with pH&gt;10 and solid particles of lead carbonate. The suspension is filtered, after which the lead carbonate is removed from the process, while the liquid phase with the Na.sup.+, OH.sup.-, CO.sub.3.sup.2-, SO.sub.4.sup.2- ions is fed to the first step of desulphurization of the oxide-sulfate fraction.
The aforementioned steps of the known method resulted in an increase in the degree of recovery of lead during the reduction smelting of the oxide-sulfate fraction by reducing the amount of the lead sulfide PbS therein which passes into slag. Due to this the emission of sulphur into the environment as sulphur dioxide SO.sub.2 is reduced. A reduction of the contamination of the environment was also due to the transition of the SO.sub.4.sup.2- ion from the oxide-sulfate fraction of the initial raw material into the Na.sub.2 SO.sub.4 solution and evaporation of the latter, as a result of which the solid Na.sub.2 SO.sub.4 fraction becomes a marketable product. As a result the efflux of the Na.sub.2 SO.sub.4 solution into drain waters is prevented.
During the realization of the known method the scarce agent NaOH is used, which is removed from the process as Na.sub.2 SO.sub.4, making the recovery of lead more expensive. Furthermore, substantial power consumption is necessary in the realization of the method for the production of anhydrous Na.sub.2 SO.sub.4, which also makes the recovery of lead more expensive. As a result of the aforementioned steps realizing the method, the degree of recovery of the lead is relatively low because of its loss together with the polymer material fraction taken out of the process. Furthermore, the metallized lead taken out of the process comprises some amount of the oxide-sulfate fraction, which remained therein after the separation. During subsequent metallurgical processing of the metallized lead, this reduces the recovery of lead into a marketable product by 1% due to its loss in the slag.